| 摘要 |
PURPOSE:To increase tenacity of a weld zone after working in high frequency bending a welded steel tube having <60kg/mm.<2> tensile strength and <=20mm. plate thickness by specifying maximum attained temperature of weld zone of the steel tube during heating. CONSTITUTION:A welded steel tube P to be worked is passed through plural pairs of guide rolls 1, 1 that restrain movement of the steel tube in radial direction, and inserted into a heating coil 2 placed front center of the rolls and a cooling ring 3 connected in a body with the coil. The rear end of the tube P is held by a tail stock 5 connected to a driving device, and the front end is fixed by a clamping jig 6 at the tip of an arm 7 supported rotatably around the basal end. A gas burner 8 that opposes to the surface of the weld zone W behind the coil 2 is provided to preheat the weld zone W. Maximum attained temperature of the weld zone W during heating is controlled to temperature range of (AC1+ AC3)/2-AC3 basing on transformation point at the time of rapid heating similar to bending of welded metal, i.e. points AC1 and AC3. Then, the stock 5 is pushed out and the tube P is bent. |
